1. Field of the Invention
The present invention relates to a perpendicular magnetic recording medium having a perpendicular magnetic film suitable for high-density magnetic recording, and a magnetic storage apparatus using the same.
2. Description of the Prior Art
In magnetic disk apparatuses that have been made practicable at present, longitudinal magnetic recording is commercialized. In the longitudinal magnetic recording, a technical objective is to form, in a longitudinal magnetic recording medium which is liable to be magnetized in the direction parallel to its disk substrate surface, longitudinal magnetic domains that are parallel to the substrate at high densities. As a method to increase the recording density of this longitudinal magnetic recording medium, there is proposed a method of using keepered media in which a very thin, soot magnetic film is formed on the surface of a recording medium having an axis of easy magnetization in the longitudinal direction.
This technique is described on page 116 (Article No. DQ-13) and page 133 (Article No. EB-12) of collected abstracts published in 41st Annual Conference of Magnetism &Magnetic Materials (Nov. 12-15, 1996), and the like.
It is stated that according to adoption of such a medium structure it is possible to use an inductive type of thin film head for recording and reading so as to improve the areal recording density of magnetic recording greater than 1 Gb/in..sup.2 In the case of the longitudinal recording system, however, the magnetization directions of adjacent recorded bits are essentially opposite to each other. Thus, even if such a technique is used, magnetization transition areas whose boundary has a certain width are formed, so that it is technically not easy to realize an areal recording density of 10 Gb/in..sup.2 or more.
On the other hand, the perpendicular magnetic recording is a method to form magnetization perpendicular to the thin film media surface, and is different from conventional longitudinal recording media in recording principles and the mechanisms of medium noises. Since adjacent magnetization directions are not opposite to each other, the perpendicular magnetic recording has attracted attention as a method suitable for high-density magnetic recording. Various structures of perpendicular media are proposed to improve the performance of magnetic recording.
In order to improve perpendicular orientation of a perpendicular magnetic film composed of, for example, Co alloy materials, investigations have been made on methods of forming an underlayer between the perpendicular magnetic film and a substrate. For example, Japanese Unexamined Patent Publication Nos. 58-77025 and 58-141435 disclose methods of forming a Ti film as an underlayer of a Co--Cr magnetic film. Japanese Unexamined Patent Publication No. 60-214417 discloses a method of using a Ge or Si material as an underlayer, and Japanese Unexamined Patent Publication No. 60-064413 discloses underlayer materials of oxides such as CoO and NiO.
Moreover, as a perpendicular magnetic recording medium which is combined with a single pole type recording head for use, investigations have been made on a medium having a soft magnetic thin film such as permalloy between its substrate and its perpendicular magnetic film.